Of the explosives used worldwide today, the ammonium nitrate explosives are the largest group. They are widespread particularly in mining. A particularly important group within the ammonium nitrate explosives in this connection are the emulsion explosives, which consist essentially of a water-(or salt)-in-oil emulsion of an aqueous solution, supersaturated at room temperature, in an oil matrix (fuel). The oil phase is the continuous phase and includes small droplets of the supersaturated solution of the oxidizing agent. In this connection, the water content of the solution can be up to below 4% by weight. The dissolved salts are metastable and have a tendency toward crystallization. If, for example, ammonium nitrate crystals form, this has unfavorable effects on the emulsion (solidification, the emulsion is no longer pumpable) and also on the cap sensitivity of the emulsion, i.e. the explosive becomes less sensitive to initial detonation. In order to keep such an emulsion stable, therefore, an emulsifier is generally required which is suitable for the preparation of water-in-oil emulsions. Because of its surface activity, it promotes emulsification of the salt phase in small droplets and prevents coalescence of the formed droplets after the emulsion has formed.
The emulsion, also called matrix, is generally still not ignitable, and therefore, in order to achieve sufficient cap sensitivity, the density of the matrix must be lowered by adding microspheres (glass bubbles), by chemical gassing or by another method, such as, for example, by adding granular ammonium nitrate. The emulsions are then in some circumstances also ignitable without boosters with blasting caps. Such emulsions are safety explosives. This technology was described for the first time in U.S. Pat. No. 3,447,978.
U.S. Pat. No. 3,447,978 discloses explosive emulsions consisting of a salt-in-oil emulsion of a supersaturated ammonium nitrate solution in an oil matrix, an emulsifier of the water-in-oil type, e.g. a sorbitan ester, fatty acid glycerides or phosphoric esters, being used as emulsifiers. These emulsifiers, however, only give emulsions with low long-term stability.
EP-A-0 155 800 discloses emulsion explosive material mixtures which comprise emulsifiers, where at least one emulsifier is strongly lipophilic and an agent for altering the electrical conductivity of the emulsion, which essentially consists of a lipophilic and of a hydrophilic component, and in which the lipophilic constituent has a chain structure derived from a polymer of a monoolefin containing 3-6 carbon atoms. In particular, reaction products of poly(isobutenyl)succinic anhydride with aminoalcohols, amines and sorbitol as emulsifiers are described.
EP-A-0 285 608 discloses water-in-oil emulsions, where the emulsifiers present are reaction products of a hydrocarbon-substituted carboxylic acid or a hydrocarbon-substituted anhydride (or an ester or amide derived therefrom) with ammonia or at least one amine, the hydrocarbon radical having on average 20-500 carbon atoms. Polymers containing two or more hydrocarbon radicals are not disclosed. Reaction products of poly(isobutenyl)succinic anhydrides with morpholine and aminoalcohols are specifically described.
The emulsifiers cited in EP-A-0 155 800 and EP-A-0 285 608 and based on polyisobutenylsuccinic anhydride (i.e. the reaction product of a long-chain, branched olefin with maleic anhydride), produce, in contrast to the emulsifiers of the first generation cited in U.S. Pat. No. 3,447,978, emulsions with high long-term stability. The base emulsifiers, however, have the disadvantage that their synthesis, because of the underlying ene reaction, requires very high temperatures (180-230xc2x0 C.) and relatively long reaction times, which leads to a high consumption of energy and correspondingly high preparation costs.
Polymers of polyisobutylene and maleic anhydride are also part of the prior art.
WO-A-90/03359 discloses polymers of polyisobutylene and maleic anhydride which, after they have been functionalized using polyamines, can be used as additives in fuels and lubricating oils. EP-A-0 831 104 discloses terpolymers of polyisobutylene, xcex1-olefins and maleic anhydride and also reaction products of these terpolymers with polyamines for analogous applications.
Surprisingly, we have now found that not only derivatives of monomeric adducts of polyisobutylene and maleic anhydride, but also derivatives of polymeric adducts of maleic anhydride and olefins having 20-500 carbon atoms, alone or mixed with other emulsifiers, are suitable as extremely effective emulsifiers for emulsion explosives. In contrast to the compounds cited in EP-A-0 155 800 and EP-A-0 285 608, these compounds have two or more hydrophobic groups and two or more hydrophilic head groups on the polymer backbone. The parent polymeric anhydrides can be prepared at a significantly lower temperature (80-150xc2x0 C.) and by free-radical copolymerization significantly more quickly than the alkenylsuccinic acid derivatives of the prior art, meaning that they have ecological and also economic advantages over the prior art. Surprisingly, despite having molecular weights which are significantly higher than those of polyisobutenylsuccinic acid derivatives, the products do not have increased viscosities, meaning that the products can be handled without problems despite the relatively high molecular weight. In this connection, the emulsifying action and emulsion stability of the products, particularly in mixtures with small amounts of coemulsifiers, correspond to at least those of the products cited in the prior art.
The invention thus provides an explosive composition consisting of
A) an oxygen-donating constituent, which forms a disperse phase,
B) an organic constituent, which forms a dispersion phase, and
C) at least one emulsifier,
wherein the emulsifier includes a copolymer comprising, in random or regular order, structural units derived from maleic anhydride and from one or more olefins having more than 40 carbon atoms, where the structural units derived from maleic anhydride have been modified by reaction with alcohols, aminoalcohols, ammonia or amines.
In the text below, the term xe2x80x9cmaleic anhydridexe2x80x9d also refers to the maleic anhydride modified in the sense given above by reaction with alcohols, aminoalcohols, ammonia or amines.
The emulsifier according to the invention comprises, in the copolymer chain, at least one olefin, preferably an xcex1-olefin having more than 40, preferably from 40 to 500, in particular from 40 to 200, carbon atoms. The copolymer may also further comprise other comonomers.
Suitable olefins for the preparation of the polymers according to the invention are olefins preferably containing a double bond in the xcex1-position or mixtures of the number of such olefins. Particular preference is given to olefins obtained by polymerization of C2-C6-monoolefins, such as, for example, polypropylenes or polyisobutylenes in the molecular weight range from, preferably, 200-5000 g/mol, and which comprise  greater than 30%, preferably  greater than 50%, particularly preferably  greater than 70%, of isomers containing a double bond in the xcex1-position, i.e., for example, containing an end group Rxe2x80x94C(xe2x95x90CH2)CH3. Such polyisobutylene grades are obtainable, for example, under the trade names Glissopal(copyright) or Ultravis(copyright). In this connection, particularly suitable polyisobutylenes are those which have a high content of isomers containing an xcex1-position double bond. Particularly suitable as olefin components are also mixtures of polyisobutylenes and straight-chain or branched-chain C10-C30-xcex1-olefins or mixtures of polyisobutylenes with alkylallyl polyglycol ethers having from 3 to 20 ethylene oxide units. In this case terpolymers of polyisobutylene, maleic anhydride and xcex1-olefin or allylmethyl polyglycol ethers form. The alkylallyl polyglycol ethers mentioned are preferably allylmethyl polyglycol ethers in the molecular weight range from 200 to 1000 g/mol.
The emulsifiers according to the invention can be synthesized by methods known per se, one description being, for example, in Oil Gas European Magazine 1996, 22, 38-40. Firstly, olefins, preferably xcex1-olefins, particularly preferably polyisobutylene or mixtures of polyisobutylene and short-chain C10-C30-xcex1-olefins or mixtures of polyisobutylene with allylalkyl polyglycol ethers and maleic anhydride are polymerized using a suitable free-radical initiator. The molar quantity ratio between maleic anhydride and the total of the other comonomers is preferably from 0.7:1 to 1.6:1. The polymerization can be carried out without a diluent, or also in a nonprotic solvent. The reaction temperature of the polymerization is between 50 and 200xc2x0 C., preferably between 80 and 160xc2x0 C. Alternating copolymers of olefin and maleic anhydride preferably form. In the second reaction step, the resulting polymer is reacted in a polymer-analogous reaction with alcohols or aminoalcohols to give polymeric half-esters, with ammonia and/or amines and, where appropriate, also with aminoalcohols, to give polymeric half-amides or imides.
Suitable alcohols for the functionalization of the maleic anhydride copolymers to give half-esters are monoalcohols having 1-6 carbon atoms, e.g. methanol, ethanol, propanols, butanols or pentanols; alkylpolyglycols are also suitable.
Suitable aminoalcohols are, for example, N,N-dimethylaminoethanol, N,N-diethylaminoethanol, N,N-dibutylaminoethanol, 3-dimethylaminopropanol, N-hydroxyethylmorpholine, monoethanolamine, diethanolamine, triethanolamine, 3-aminopropanol, isopropanolamine and 2-(2-aminoethoxy)ethanol. The half-ester formation is carried out at 30 to 150xc2x0 C., preferably at 50 to 100xc2x0 C. In order to avoid crosslinking reactions, aminoalcohols with a tertiary amine nitrogen and a hydroxyl function, such as dimethylaminoethanol, diethylaminoethanol or N-hydroxyethylmorpholine, are particularly preferred.
Suitable amines for the functionalization of the maleic anhydride copolymers are monoamines with a primary or secondary amino function, such as methylamine, ethylamine, butylamine, laurylamine, coconut fatty amine, stearylamine, dimethylamine, diethylamine, dibutylamine etc., but also di- and polyamines, e.g. 3-dimethylaminopropylamine, 3-diethylaminopropylamine or 3-morpholinopropylamine.
Preferred amines contain only one condensable alcohol or amino group in order to prevent crosslinking of the individual polymer units. Using the amines listed, olefin/MA copolymers (MA=maleic anhydride) functionalized to the half-amide are obtained at reaction temperatures of at most 50-60xc2x0 C. Above 50xc2x0 C., imide formation arises to an increased extent, meaning that, should olefin/MA copolymers functionalized to the imide be desired, it is preferable to carry out the reaction in the temperature range from about 50 to about 150xc2x0 C.
The reactions to give the half-esters, half-amides and imides can be carried out either without a diluent, or else in a solvent, preferably in the mineral oil used for formation of the explosive emulsion. The latter is particularly preferred, in cases where the viscosity of the emulsifier permits it.
The emulsifiers according to the invention can be mixed with any common emulsifier. Preferred mixing components are the water-in-oil emulsifiers used in U.S. Pat. No. 3,447,978, such as sorbitan monooleate, glycerides, phosphoric esters, etc., but also amidoamines/imidazolines obtainable by condensation of fatty acids with polyamines. Particular preference is given to mixtures of the emulsifiers according to the invention with the monomeric emulsifiers specified in EP-A-0 155 800 and EP-A-0 285 608, i.e. with derivatives of alkenylsuccinic anhydrides, such as polyisobutenylsuccinic anhydride, i.e. half-esters, half-amides, imides and salts thereof with amines and alkali metals.
The emulsifiers according to the invention are suitable for use as constituent C in the explosive compositions (emulsion explosives) of the invention. The salt phase of the emulsion explosive (constituent A) consists of a supersaturated solution of an oxygen-releasing salt, ammonium nitrate preferably being used. Other oxygen-releasing salts, e.g. other nitrates such as sodium or potassium nitrate, and also perchlorates can also be used as additives.
The oil phase (constituent B) used is generally a mineral oil, in particular a paraffin mineral oil. It is also possible to use naphthene-based oils, vegetable oils, used oil or diesel oil. The emulsifiers used are mostly predissolved in the oil phase. The emulsifiers can be used as concentrate (up to 100% of active substance) or else as solution in a suitable oil, in cases where the inherent viscosity of the emulsifier is too high.
Further auxiliaries are bodying agents such as waxes, paraffins or elastomers, in cases where the intention is to prepare cartridged explosive, products which are said to increase the water resistance of the emulsion, such as silicone oils, but also other emulsion stabilizers, thickeners or antioxidants, which are intended to prevent aging of the emulsifier.
The explosive emulsion generally comprises 20-97% by weight, preferably 30-95% by weight, particularly preferably 70-95% by weight, of the discontinuous phase (i.e. predominantly water and ammonium nitrate with the other water-soluble additives), and the water content varies in the range 2-30%, preferably in the range 4-20%. The oil phase (including the additives dissolved therein) includes about 1-20% by weight of the overall composition, but preferably 1-10%. The content of emulsifier in the overall composition is in the range 0.2-5% by weight, preferably in the range 0.4-3%.
The explosive emulsions are preferably prepared using common emulsifying processes. Firstly, a supersaturated ammonium nitrate solution (optionally with the addition of other water-soluble auxiliaries listed above) at 80-100xc2x0 C. is prepared and heated until all solids are dissolved, and, if necessary, the solution is filtered to remove insoluble material. In parallel, a solution of the emulsifier in the oil matrix (likewise with the addition of other oil-soluble auxiliaries such as waxes, paraffins, antioxidants etc.), likewise at 50-100xc2x0 C., is prepared. Then, with stirring, the salt melt is preferably added to the oil/emulsifier mixture, but the reverse procedure is also possible. Vigorous stirring increases emulsion formation. The entrainment of seed crystals into the emulsion must be avoided. Where appropriate, other components, such as microballoons (glass bubbles), solids such as TNT, solid fuels such as aluminum or sulfur, inert materials such as baryte or sodium chloride, or undissolved ammonium nitrate are then added, and the mixture is stirred until the solids are distributed homogeneously. Chemical gassing involves adding, for example, thiourea and sodium nitrite, which leads to gassing of the emulsion within a certain period. In industry, the emulsification stage can be carried out in special mixers and, where appropriate, using static mixers.
The invention further provides a terpolymer comprising monomer units derived from
A) an olefin having more than 40 carbon atoms,
B) maleic anhydride, and
C) an alkylallyl polyglycol ether of the formula
Rxe2x80x94(OCH2CH2)nOxe2x80x94CH2xe2x80x94CHxe2x95x90CH2
where n=3-20 and R=C1-C4-alkyl.
The olefin preferably has from 40 to 500, in particular from 40 to 200, carbon atoms. It is preferably an xcex1-olefin, particularly preferably a polyisobutene. A particularly preferred embodiment relates to modified terpolymers obtained by polymer-analogous reaction of the said terpolymers with alcohols, amines and aminoalcohols. The terpolymers according to the invention are used as emulsifiers in explosive compositions.
Particularly preferred terpolymers comprise monomer units of
A) 18 to 70 mol % of polyisobutene
B) 25 to 80 mol % of maleic anhydride
C) 2 to 15 mol % of allyl polyglycol ether.
As the experimental examples listed below demonstrate, the polymeric emulsifiers according to the invention, alone or in particular in a mixture with other emulsifiers, such as, for example, sorbitan esters, exhibit identical emulsion stabilities to a conventional polyisobutenylsuccinic acid derivative. It is interesting that the functionalization of the polymeric anhydride, at least in mixtures with other emulsifiers, is not absolutely necessary. Under the conditions of the emulsification, the corresponding amide presumably forms from the anhydride and ammonium nitrate in situ.